Method for the preparation of faujasite-type zeolites

ABSTRACT

FAUJASITE-TYPE ZEOLITES HAVING HIGH SIO2/AL2O3 RATIOS ARE PREPARED BY THE ACIDIFICATION OF THE REACTION MIXTURE INTERMEDIATE AN INTIAL HOLDING PERIOD AND A SECOND HOLDING PERIOD. SUITABLE SOURCES OF SILICA INCLUDE SODIUM SILICATE, SILICA GEL, AND SILICIC ACID. CRYSTALLINE ALUMINOSILICATE ZEOLITES, SUCH AS CLINOPTILOLITE, MAY BE EMPLOYED AS SOURCES OF BOTH SILICA AND ALUMINA. A PROMOTER, SUCH AS SODIUM CHLORIDE, IS OPTIONALLY ADDED TO THE REACTION MIXTURE.

United States Patent Oflice 3,701,629 Patented o... 31, 1972 3,701,629 1 METHOD FOR THEPREPARATION F FAUJASITE-TY PE ZEOLITES Dale D. Maness, Austin, Tex., assignor to Esso Research and Engineering Company No Drawing. Filed Aug. 4, 1971, Ser. No. 169,069 Int. Cl. C01b 33/28 U.S. Cl. 423-329 6 Claims ABSTRACT OF THE DISCLOSURE v Faujasite-type zeolites having high SiO /Al O ratios are prepared by the acidification of the reaction mixture intermediate an initial holding period and a second 'holding period. Suitable sources of silica include sodium silicate, silica gel, and silicic acid. Crystalline aluminosilicate zeolites, such as clinoptilolite, may be employed as sources of both silica and alumina. A promoter, such as sodium chloride, is optionally added to the reaction mixture.

FIELD OF THE INVENTION BACKGROUND OF THE INVENTION Various processes for the preparation of crystalline aluminosilicate zeolites from silica and aluminum-con taining materials have heretofore been proposed. Thus, for example, crystalline aluminosilicate zeolites having a silica to alumina mole ratio of about 2.5 to about3.5 can be readily prepared by methods which in general involve digesting aqueous solutions of sodium silicate and'sodiurn aluminate at elevated temperatures. The raw materials required for manufacturing these low-silica; crystalline aluminosilicate zeolites are relatively inexpensive; Previous attempts to prepare high-silica, crystalline alumina-1 silicate zeolites, i.e. having silica to alumina mole ratios, greater than about 4.0, directly from inexpensive sources of silica, eg. sodium silicate solutions, have however met with difliculty, see US. Pat. 3,227,660, column 2, and 3,484,194. In addition, such zeolites have recently been prepared from other crystalline aluminosilicate zeolites, as is disclosed in application Ser. No. 104,745 filed on Jan. 7, 1971, quite sucscessfully, but such processes have not always resulted in the preparation of crystalline aluminosilicate zeolites having as high a silica to alumina mole ratio as is desirable. One of the well known methods for the manufacture of high-silica crystalline aluminosilicate zeolites requires a silicahydrosolas the major starting material. These hydrosols, as exemplified by the commercial Ludox, are prepared by extensive ion exchanging of sodium silicate solutions. This procedure is quite expensive and thus the resulting silica hydrosols are several times as costly as sodium silicate, on an equivalent SiO basis. Thus, for example, in U.S. Pat. 3,130,007, when it was desired to prepare a crystalline aluminosilicate having a silica, to alumina mole ratio greater than 3.9, silica sources such as expensive aqueous colloidal silica solswerenecessary as the major sources of silica.

Another method for producing crystallin aluminosilicate zeolites is described in US. Pat. 3,227,660. In

this process, the patentees use sodium silicate as the major starting material, but need to convert it to a silica hydrogel by conventional methods, i.e. by acidifying a sodium silicate solution to a pH below about 10, and washing and partially drying the resulting hydrogel. Thus, in order to obtain high silica to alumina mole ratio products, the patentees found it necessary to use an added peptizing step wherein the silica hydrogel was partially peptized in an aqueous sodium hydroxide solution at an ambient temperature of, e..g., about 10 to 50 C., for up to about 3 hours. The final product contained only about 35 to 70% by weight of the desired high-silica, crystalline aluminosilicate zeolite.

In addition, application Ser. No. 104,745, referred to hereinbefore, recently disclosed a valuable and inexpensive method for preparing such crystalline aluminosilicate zeolites utilizing other crystalline aluminosilicate zeolites as starting materials. This process utilizies alkali metal hydroxide solutions to convert the initial crystalline aluminosilicate zeolite materials, but is limited in the silica/ alumina mole ratio of the product obtainable.

It is thus quite apparent that all these prior art processes demonstrate the difficulty encountered in preparing crystalline aluminosilicate zeolites of high purity and having silica to alumina mole ratios greater than about 4.0 inexpensively and in high yields.

SUMMARY OF THE INVENTION In accordance with the present invention, it has been discovered that crystalline aluminosilicate zeolites of the faujasite type, and having silica to alumina mole ratios of at least about 4.0, can be prepared by the acidification of the zeolite-forming reaction mixture at a specific time during the. zeolite preparation procedure. Further in accordance with the present invention, these high-silica crystalline aluminosilicate zeolite products may be utilized in various hydrocarbon conversion process.

DETAILED DESCRIPTION The crystalline zeolite preparation procedure of the present invention primarily consists of preparing a reaction mixturecontaining a source of silica, a source of alumina, a source of alkali metal oxide, and water, and may also include a promoter such as sodium chloride. The reaction mixture i then generally put into solution and thoroughly mixed at ambient temperature, and heated to a temperature generally of from about to about 150 C. Pressure must be applied at temperatures above C. to prevent substantial loss of water from the reaction mixture. In the standard procedures employing such reaction mixtures for preparing crystalline aluminosilicate zeolites,

these conventional mixtures have then generally been held at these high temperatures for a sufiicient time to form a crystallized product. In the present invention, however, during this initial holding period the reaction mixture is acidified to a Na O/SiO ratio of from 0.25 to about 0.40, preferably 0.32 to 0.38, and most preferably 0.34 to 0.36.

s t The reaction mixture is then again held at the above noted temperatures during a second holding period for a further time in order to produce the crystalline zeolitic product.

In such procedures where the major source of silica in the reaction mixture is sodium silicate, silica gel or silicic acid, the reaction mixture will have a composition expressed in terms of oxide-mole ratios falling within the following ranges:

reaction mixture, the ratio of NaCl to A1 in the mixture will generally be from about 0.5 to 5, preferably about 1.4. This mixture is then maintained at a temperature in the gist, vol. 45, 1960, at pages 351-369, in an article by F. A.

-Mumpton, which includes a review of the X-ray diffraction pattern of a clinoptilolite sample from Mount Hector, Calif.

range of from about 25 to 150 C., preferably 80 to 5 In order to prepare this faujasite product according to 130 C.,' and most preferably from about 90 to about the present invention, utilizing the clinoptilolite as a start- 110 C. for a period of from 0.5 to about 5 hours, prefering material, an initial reaction mixture is prepared by ably about 1 to 2 hours, most preferably about 1 /2 hours, blending the clinoptilolite with an alkali metal hydroxide at which time the solution is acidified to a Na O/SiO in aqueous solution, such that the ratio of H O/zeolite emratio of from 0.25 to about 0.40, preferably from 0.32 to ployed will be from between about 0.3 g./g. to about 2.0 0.38 and most preferably from 0.34 to 0.36. This composig./g., preferably from 0.5 to 1.5 g./ g. and most preferably tion is then further maintained at a temperature in the from 0.9 to 1.1 g./ g. The alkali metal hydroxide concenrange of from about 90 to about 110 C. for a period of tration will be such as to comprise from 10 to 50% NaOH from about 40 to about 231 hours, preferably ,64 to 159 and preferably from 20 to 35% NaOH, thus giving a mole hours, and most preferably 90 to 110 hours. ratio of Na O/SiO .in terms of mole ratios of oxides, in

In the process of the present invention wherein the the initial reaction mixture of from 0.20 to about 1.2, prefsources of both silica and alumina comprise an initial erably from 0.40 to about 0.50. i crystalline aluminosilicate zeolite, and the initial reaction This reaction mixture will then be heated to a temperamixture includes an aqueous alkali metal hydroxide soluture of from 90 to 110 C., and maintained at that tion, generally utilizing high concentrations of alkali solutemperature fora period of from 0.5 to 2.5 hours, prefertion, preferably from 10 to 50% NaOH, and most preferably 1 to 2 hours. ably from 20 to 35 NaOH, this initial reaction mixture I The mixture will then be acidified by the addition of is maintained at from about to 150 C., preferably an acid, such as HCl, to provide a reaction mixture hav- 80". to 130 'C., and most preferably from 90 to 110 C=, ing a Na O/SiO mole ratio of from 0.30 to about for an initial period of from 0.5 to about 2.5 hours, prefer- 25 0.45, preferably from 0.34 to 0.36, and most preferably ably from 1 to 2 hours, and most preferably about 1.5 of about 0.35. This reaction mixture will then be mainhours, at which time this solution is acidified to-a tained at a temperature of from 90 to 110 C., for a Na o/sio period of from 15 to 17 hours, thus producing a crystallized famasrte-type crystalline alumino-sillcate zeolite havmole ratio of from 0.30 to about 0.45, preferably from i a SiQ /A1 O l ratio greater h about 4, refer. to and most Preferably from to This ably from 4.2 to 4.8, and thus a unit cell size less than solution is then additionally maintained at similar temperabout 2430 angstroms, and f bl from 24,77 to atures for a further period of from 8 to hours, prefer- 2 5 angstroms 1 y from 10 to 24 hours, and most Preferably from 15 i The following examples are representative of the procto 17 hours, until the final crystallized product is formed. 35 asses f the present invention This product, preferably being of the faujasite type, will have a siO /Al og, mole ratio greater than about 4, Example 1 preferably from about 4.2 to about 4.5, and most prefer- In order to further demonstrate the applicability of ably greater than about 4.9. i the present process to the preparation of faujasite from The acidification step previously described will generally 40 the initial crystalline aluminosilicate zeolite clinoptilolite, be carried out by the addition of an inorganic acid to several runs were carried out with varying degrees of the reaction mixture, preferably acids such as HCl, HNO acidification according to the present process. The data HBr and HCN, and most preferably an inorganic acid such obtained are contained in Table 1. In each of these runs, as HCl. initially 10 grams of clinoptilolite was mixed well with DESCRIPTION OF THE PREFERRED 7 i P 6 Vt/Percent .NaOH EMBODIMENT solution. This nitial reaction mixture was then placed in a 4 ounce bottle, capped, and immersed in a 100 C. In an extl'emelylmpoftam aPpllcatlon of the Present oil bath. The bottle was withdrawn from the bath and invention, the silica and alumina in the initial reaction led to room temperature ri r't 'a idifi ti and mixture are pP y the initial Crystalline aluminosilithen r'e-capped and returned to the oil bath for the second Cate zeolite p ite, one of the most abundant holding period. Also in these runs, acidification was carnaturally-occurring zeolites, and treatment according to ried out after the initial holding period of 1- /2 hours, and the process of the present invention results in the synthesis after acidification, a second holding period of 16 hours of a faujasite-type product having a silica/alumina mole wasm lo ed, TABLE 1 Products NazO/SIO: Crystal- Initial zeolite Added acid acldificai ib ii Faujasite eigit fi 0.47 N ne Yes 102 24.80 3.9 0.41 1.30 mls. of 12.N HCl 0. 45 Yes 99 24. 768 4.19 o. 47 2.28 mls. or 12 N H01 0.35 Yes 90 24. 704 4. 09 0. 47 3.25 11115. 0i 12 N H01 0. 3 Yes 15 Too weak to measure 1 Clinoptilolite from Mount Hector, Calif.

ratio greater than about 4, thus having a unit cell size Example 2 below about 24.08 angstroms.

Clinoptilolite is an extremely abundant natural crystalline aluminosilicate zeolite which has not been found useful for purposes of the adsorption or catalysis of hydrocarbons heretofore. The reason for this is the very low surface area of this material, and its concomitant lack of adsorptive capacity, irrespective of its high silica to alumina molar ratio of about 11. A review of the characteristics of this material appears in the American Minerolo In order to determine the optimum length of time for the initial holding period, i.e. prior to acidification, several additional runso'f varying initial holding periods were carried out in 'a manner similar to that described in Example 1, and the results are contained in Table 2.

' These results indicate that an initial holding period of from 1 to 2 hours, and preferably of about 1 /2 hours, is most desirable for preparing a faujasite product of high SiO /Al mole ratio and of a high degree of crystal- Example Y- In order to further demonstrate the scope of the present TABLE 2 Products (Initial) Initial hold- NazO/SiOz Crystal- N820] ing period at after acidifllinity, Unit cell S102] S102 Added acid 100 0., hrs. cation Faujasite percent size, A. A1 0;

0. 47 None Yes 102 24. 80 3.9

0. 47 2.2%11i5. 12 N 1 0. 35 Yes 47 24. 708 4. 66 134 0. 35 90 24. 704 4. es -2 0. 35 36 24. 678 4. 82 2% 0.35 Yes 23 Too weak to measure 3 0.35 Yes 30 Too weak to measure l Clinoptilolite from Mount Hector, Calif.

Example 3 invention, several additional runs similar to those shown in Examples 3 and 4 were carried'out, but at a constant In order to further demonstrate the scope of the presinitial holding period, at 100 (3., for two hours, and at ent invention, several runs were carried Out in which a varying second holding periods, The results of these runs faujasite-type zeolite product was prepared using sodium are contained in Table 5.

"' TABLE 5 Products (Initial) NazO/SiO: Second Crystal- NBzO/ after holding iinity, Unit cell 8102/ SiOz Added acid acidification period, hrs. Faujasite percent size, A. A110;

22 0.00 RN 0.35 24.755 4.29 23 0.60 Same. 0. Z74 24.704 4,50 0. 60 0. as .90 24. see 4. 99 0. 35 112 24. 053 11. 09 0. as 56 24. 909 a. 09

silicate solution as the source of silica, as per D. W. Brcck Obviously, many modifications and variations of this In US invention may be made without departing from the The general procedure employed in these runs for the 35 ssenc andso o formation of the 1n1t1al reactlon mixture mcluded the e e c pe there and only Such hmltatlons use of grams of A12O3 3H2O as the Source of should be applied as are indicated from the appended mina, 1,231 grams of a sodium silicate solution as the claimssource of silica, 140 grams of NaOH, 50 grams of NaCl What is claimed is:

and grams of Water- 1. A method for preparing faujasite-type zeolites which The data contained in Table 3 was obtained after an initiai holding Period of two hours at C. Run #11 comprises preparing an 1n1t1al aqueous reaction mixture,

is with no acidification as Per the present invention, the major source of silica in said reaction mixture being was carried out utilizing a mole ratio of Na O/SiO of supplied by sodium silicate, silica gel or silicic acid, said 0.6, which is the lowest such ratio taught by Breck in reaction mixture having a composition, expressed in terms US. Pat. 3,130,007 (see column 3, line 30).

TABLE 3 Products (Initial) Nam/s10, Crystal- NazO/ after acidilinity, Unit cell 8102/ SiOz Added acid flcation Faujasite percent size, A. A120;

11 0.6 None Yes 200 24.97 3.0 12 0.6 19 12 N 0. 35 Yes 74 24. 704 4. 69

13 0.0 25 12 N 0.30 Yes 34 Too Weak to measure 14 0.6 27 m s '12N 0.25 Yes 18 Too weak to measure Example 4 of mole ratios of oxides, falling within the following In order to determine the optimum length of time for ranges: the initial holding period, i.e., prior to acidification, N k 2 several additional runs of varying initial holding periods 5102/ 2 3 were carried out in a manner similar to that described HBO/N320 12-90 in Example 3, and the results obtained are contained in maintaining said reaction mixture at a temperature in the Table 4. range of from about 25 to 150 C. for an initial holding TABLE 4 Products (Initial) Initial holding NazO/SiOz Crystal- N 820/ period at after acidllinity, Unit cell S102] SiO Added acid 100 0., hrs. flcatiou Faujasite percent size, A. A1 0,

0 0. 35 Yes 5 Too weak to measure 1 24 Too Weak to measure 2 24. 755 4.29 3 57 24. 759 4.26 4 67 24.700 4. 72 1s 19 24.671 4. 96 21% 198 24. 979 3. 0

perature in the range of from about 90: C. to about 110 C., and recovering a crystallized prodiic'tl" 2. The method of claim 1 wherein W aid initial reaction mixture contains NaCl in an vamountsuch that the mole ratio of NaClto, A1 0 is from about 0.5 to 5.0.

3. The method of claim 1 wherein said initial reaction mixture has a compositiohj'i expressed in terms of fr'nole ratios of oxides, falling within the following ranges;

4. The method of claim 1-wherein saidinitial reaction mixture has a composition, expressed in 'termsbf r'nole ratios of oxides, falling within the following ranges?" 8 Na o/sio -t "1.9-2.1 SiO /Al 0 110 H o/Na o 40-90 5. The method of claim 1 wherein said initial reaction mixture is maintained at a temperature of from to C. 6. The method of claim 1 wherein said initialholding period is from 1 to 2 hours.

References Cited UNITED STATES PATENTS Mason 231l2 R 3,101,251 8/1963 Howell 23113 3,130,007 4/1964 Brec k 23- 113 3,227,660 1/1966 Hansford 252'455 Z Robson 23-113 ERO QI l L Y Examiner H -U.'s. C1.X.R. 

